Conventionally, there has been disclosed a technology in which capacitors are serially connected between output terminals of an Alternating-Current/Direct-Current (AC/DC) converter, which converts the voltage of an AC power supply into a DC voltage and operates its control by generating a middle-level output voltage, so as to improve the power factor of the AC/DC converter. The AC/DC converter has a configuration for stepping up or stepping down the output voltage by using a current flowing into a boost inductor. When a polarity of the voltage of the AC power supply is inverted, a direction of the current flowing into the boost inductor is changed, and thus there has been desired an AC/DC converter that is appropriately controlled in accordance with the inversion of the polarity of the voltage.